(a) Field of the Disclosure
The present disclosure relates to automatic transmissions for vehicles. More particularly, the present disclosure relates to a planetary gear train of an automatic transmission for a vehicle.
(b) Description of the Related Art
In general, in the field of automatic transmissions, research has been performed into multi-stage speed changes in order to reduce vehicle fuel consumption and to maximize drivability. Increasing oil prices may make enhancing vehicle fuel consumption more important.
Accordingly, research in the field of engines has been performed to reduce weight and fuel consumption through down-sizing. Research has also been performed in the field of automatic transmissions to simultaneously ensure drivability and fuel consumption competitiveness through multi-stage speed changes.
However, in an automatic transmission, if the number of speed change stages is increased, the number of internal components, particularly the number of planetary gear sets, is also increased. This leads to an increase in the number of electric transmission devices, which results in deterioration of mounting characteristics and power delivery efficiency as well as an increase in production cost and weight. In recent years, automatic transmissions have been mounted in vehicles to implement the change of eight speeds or more. However, conventional automatic transmissions having greater than eight speeds include—three or four planetary gear sets and five or six control elements (frictional elements). This leads to an increased size of the transmission, which inevitably deteriorates its mounting characteristics.
Accordingly, in recent years, in order to obtain multi-stage speed changes in an automatic transmission, a double row structure for disposing planetary gear sets have been attempted. Employing dog clutches instead of wet control elements has also been attempted. However, the applicability of such a structure is limited and using dog clutches may deteriorate the speed change quality.
The above information disclosed in this Background section is only to enhance understanding of the background of the disclosure. Therefore, the background may contain information that is not prior art, which is already known in this country to a person of ordinary skill in the art.